In small precision gear units, it is common to support the shafts on bearings between parallel spaced-apart support plates. Commonly, race-type miniature bearings are used, such as ball bearings, which must be accurately located and positioned in the support plate. Commonly, the openings for the bearing races are made in a punch press in which it is possible to hold close center-to-center distances. However, in a punch press it is considerably more difficult to hold very close tolerances for the diameter of the bearing openings. Accordingly, it has been necessary to form a punched opening which is slightly smaller than desired, and then, in a second operation, to ream the hole to the precise size required for press fitting the bearing assembly into the opening. The tolerances which must be held are particularly critical where a small precision ball bearing is to be press fitted into the opening, and the opening must therefore be very close or an interference fit. The maximum allowable pressing forces must not be exceeded, otherwise the bearing may be distorted, or the bearing moved off center, or both. Additionally, the reaming or finishing step provides an opportunity for the precise center-to-center distance to be displaced.
A further problem in fitting bearings into bearing support plates resides in the fact that the bearing manufacturers provide bearings having nominal O. D. sizes, but these sizes vary within certain tolerance limits, and these tolerance limits may exceed the tolerances which the bearing manufacturers themselves specify for the plate opening, to provide a good press fit. In other words, in precision units, it may be necessary to hand-size or select the bearings so that the tolerances between the O. D. of the bearing and the I. D. of the hole in the plate are not exceeded.